Note: This article assumes you have Brightmail Gateway
When you try to send an email to a particular Exchange Distribution group Group@domain.com the result is either users don’t exist or you might get the following error if you test with Microsoft Test connectivity online tool.
The server returned status code 554 – Transaction failed. The server response was: 5.7.1 Delivery not authorized
Other related errors
‘554 5.7.1: You are not allowed to connect’
Because the group has been cached in the Symantec gateway with its old members, The result could be an error that users don’t exist or delivery is not authorized.
To solve this problem, You need to go to Brightmail gateway Administration > Directory Integration and click on your AD Directory > Advanced and hit on Clear Cache.
This would cleared the cached group and take the most recently updated group and its members.
This should resolve the problem.
How to clear the DDS cache in Messaging Gateway